Field of the Disclosure
The present disclosure is related to methods for forming conformal, porous, electrochemically active lithium manganese oxide (LixMnyOz) layers and to lithium manganese oxide layers thus obtained.
The present disclosure is further related to methods for forming conformal, porous lithium manganese oxide electrode layers, and to methods for fabricating lithium-ion batteries having a conformal, porous lithium manganese oxide layer as an electrode layer.
Technical Background
Lithium manganese oxide (LixMnyOz) has intensively been studied as an electrode material for lithium-ion batteries and is commercially used. It has a high redox potential, a competitive capacity (145 mAh/g) when cycled between 3.5 and 4.5 V versus Li+/Li and a low toxicity.
Lithium-ion batteries are typically particle-based and contain a particle-based active electrode, e.g. a particle-based lithium manganese oxide electrode. However, thin film lithium-ion batteries, based on a thin film stack and having a thin film electrode, in particular solid-state thin film lithium-ion batteries, are gaining more and more interest. In order to increase the substrate surface area and hence increase the battery capacity of such thin film batteries, the complete thin film stack may be coated on a 3D structure such as for example on a substrate comprising an array of high aspect-ratio micro-pillars.
Different deposition techniques for thin films of lithium manganese oxide have been proposed in literature, such as RF-sputtering, electrospray deposition and pulsed laser deposition. These deposition techniques are known to be rather expensive and their use does not result in a good conformality of the deposited film, which is a challenge when working with high aspect-ratio structures (e.g. 3D silicon micro-pillars).
Moreover, after the lithium manganese oxide thin film deposition, annealing at high temperature, i.e. at a temperature of at least 700° C., typically at a temperature of 750° C. to 850° C., is required to crystallize the film and to make it electrochemically active, i.e. capable of Li insertion and extraction. This annealing causes the formation of a very dense and crystalline film. The high density of the film leads to non-released mechanical strain during battery charging and discharging, which can cause the formation of cracks in the lithium manganese oxide electrode layer, loss of contact with an underlying current collector and, in case of a solid-state battery, to cracks in the solid electrolyte layer. Annealing at high temperature may also affect the underlying layers such as the current collector and/or the substrate.